The ongoing 3GPP Rel-13 study item “Licensed-Assisted Access” (LAA) intends to allow LTE equipment to also operate in the unlicensed 5 GHz radio spectrum. The unlicensed 5 GHz spectrum is used as a complement to the licensed spectrum. Accordingly, devices connect in the licensed spectrum (primary cell or PCell) and use carrier aggregation to benefit from additional transmission capacity in the unlicensed spectrum (secondary cell or SCell). To reduce the changes required for aggregating licensed and unlicensed spectrum, the LTE frame timing in the primary cell is simultaneously used in the secondary cell.
Regulatory requirements, however, may not permit transmissions in the unlicensed spectrum without prior channel sensing. Since the unlicensed spectrum must be shared with other radios of similar or dissimilar wireless technologies, a so called listen-before-talk (LBT) method needs to be applied. LBT involves sensing the medium for a pre-defined minimum amount of time and backing off if the channel is busy. Today, the unlicensed 5 GHz spectrum is mainly used by equipment implementing the IEEE 802.11 Wireless Local Area Network (WLAN) standard. This standard is known under its marketing brand “Wi-Fi.”
Due to the LBT procedure, the first slot in which the LAA SCell or LAA User Equipment (UE) is permitted to transmit cannot be predicted in advance. This makes it difficult to pre-compute the data payload since several parameters are currently dependent on the slot number in which data is transmitted.
In the unlicensed band, a node performs LBT for accessing the channel for transmission. In downlink, an E-UTRAN Node B (eNB or eNodeB) performs LBT and upon its success, downlink transmission is permitted and can be initiated to one or multiple UEs. In uplink, different UEs perform LBT individually and hence compete with each other in accessing the unlicensed channel which may be inefficient, especially in high load systems with a large number of users each having small amounts of data to transmit, resulting in collisions and a highly congested and inefficient system. Another consequence is that if an eNB schedules two UEs simultaneously at the same time but on different physical resource blocks (PRB), those UEs would compete with each other to access the channel. Hence multi-user scheduling for uplink transmission will be problematic and inefficient.
The approaches described in the Background section could be pursued, but are not necessarily approaches that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, the approaches described in the Background section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in the Background section.